This invention relates generally to the field of magnetic data storage devices, and more particularly, but not by way of limitation, to a self-contained apparatus and associated method for writing servo data to a recordable disc without use of an external reference.
Hard disc drives are used in modern computer systems to enable users to store and retrieve vast amounts of data in a fast and efficient manner.
In a typical disc drive, one or more magnetic discs are rotated at a constant high speed and accessed by a rotary actuator assembly having a plurality of read/write heads that fly adjacent the surfaces of the discs on air bearings established by air currents set up by the rotation of the discs. Each head includes a write element that selectively magnetizes data fields defined on tracks on the corresponding disc surface during a write operation, and a read element that detects the selective magnetization of the data fields during a read operation. A read/write channel and an interface circuit, responsive to the heads, are provided to transfer the data between the discs and a host computer in which the disc drive is mounted.
A closed loop digital servo system is used to control the position of the heads relative to the tracks through the application of current to a coil of a voice coil motor. The tracks are defined from servo information written to servo fields on the surfaces of the discs during manufacturing using a highly precise servo track writing procedures. The servo information is stored in a series of servo fields, the leading edges of which are radially aligned on each of the surfaces of the discs so as to define servo wedges which outwardly extend from the inner radii of the discs like spokes of a wheel. The data fields are subsequently arranged between adjacent servo fields during a disc drive formatting operation. Typical disc drives generally provide from about 30 to 90 servo wedges on each disc surface.
The servo information typically includes automatic gain control (AGC), synchronization, track address, angular position (index) and radial position information stored in associated fields, with the AGC and synchronization information providing timing and amplitude inputs, the track address information indicating the radial position of the heads, the index information indicating the angular position of the heads with respect to the discs and the position information indicating the position of the heads with respect to the center associated tracks on the discs. Thus, during normal disc drive operation, the servo information is periodically sampled to enable the servo system to control the position of the heads to properly effectuate the transfer of data between the data fields and the host computer.
Because servo tracks contain the information necessary to locate, write or read data on the recording member, the servo tracks are typically written during manufacture by a separate servo track writer apparatus. Servo track writers include components that control and monitor the radial and angular position of the read/write heads in the absence of preexisting address information by relying on internal or external reference position references.
The angular position of the rotating disc with respect to the read/write head is typically monitored through use of an externally mounted clock head assembly. The clock head is typically inserted through an aperture in the basedeck of the disc drive (in a clean room environment) so as to be in close proximity with the surface of the disc at its outer diameter. Once located, a control circuit instructs the clock head to write a clock track on the disc surface while the disc is rotating at a selected speed. The clock track comprises a sequence of alternating pulses at a selected frequency which are subsequently read by the clock head to generate a reference clock signal used to control the timing of the servo track writing operation.
Once the clock track has been written, the servo track writer can adjust the radial position of the read/write heads. There have been a variety of approaches to radial positioning in servo track writing. One such approach involves the use of a mechanical xe2x80x9cpush-pinxe2x80x9d assembly. A push-pin servo track writer includes a pusher pin which extends upwardly through an aperture in the basedeck in order to engage the actuator arms. In many embodiments, the pusher pin advances the actuator arms in response to a closed-loop servo control based on a master encoder disc located on the external servo track writer. Alternatively, the closed-loop servo control of the pusher pin can be established through use of a laser-based detector. When a laser detector is employed, a laser mounted on the servo track writer monitors the position of a reflective surface located on the actuator assembly inside the disc drive relative to an optical detector located inside the servo track writer.
While effective, push-pin servo track writers require that an aperture be formed in the basedeck. Mechanical push-pin servo track writers are also limited in their accuracy by adverse mechanical resonance. A less invasive approach has been suggested whereby a control circuit directs the application of current to the internal voice coil motor (xe2x80x9cVCMxe2x80x9d) to position the read/write heads in reference to feedback generated by a conventional optical detector located on the servo track writer. This xe2x80x9copticalxe2x80x9d pusher pin approach benefits from having fewer mechanical assemblies and from a reduction in the number of necessary apertures in the disc drive.
Despite the aforementioned advances, servo track writers of the present generation are expensive to manufacture, time intensive and require that servo track writing be performed in clean room environment. In light of these prior art deficiencies, a need continues to exist for an improved method and apparatus for writing servo data in a disc drive.
The present invention is directed to a self-contained apparatus and associated method for writing servo information to a disc drive.
In accordance with a preferred embodiment, the disc drive comprises a rotatable disc upon which servo information is stored, the servo information used to control the position of a rotary actuator, which supports a read/write head adjacent the disc.
An internally mounted clock head assembly provides angular position information by writing and reading a clock track signal on a portion of the disc not accessed during user operation. The clock track signal comprises a series of alternating pulses occurring at a selected frequency.
A radial position detection assembly also contained within the disc drive provides the radial position information. The radial position detection assembly is used to register movement of the rotary actuator in the absence of preexisting servo information. The radial position detection assembly comprises a light source, a detector and a reflective member with diffraction grating. Preferably, the reflective member is adhered to a rear portion of the rotary actuator.
The servo information is written to the disc by connecting the disc drive to a host computer, writing the clock track signal, calibrating the radial position detection assembly and writing the servo information in relation to the angular and radial position information output by the respective clock track and radial position detection assemblies.